Preterm Birth

Preterm birth is defined as birth occurring before 37 weeks of pregnancy or more than three weeks early. It is divided up into mildly preterm (32-37 weeks), moderately preterm (28-31 weeks) and extremely preterm (before 28 weeks).

By
Hannah Dahlen

In Australia around 16,000 babies are born preterm each year (6-7percent of births). Preterm birth is defined as birth occurring before 37 weeks of pregnancy or more than three weeks early. It is divided up into mildly preterm (32-37 weeks), moderately preterm (28-31 weeks) and extremely preterm (before 28 weeks). Disappointingly the rate of preterm birth has not really changed in over 20 years and there are concerns that it is in fact on the rise in Australia.

Who is at risk of preterm birth?

It is not easy to predict who will go into premature labour and who will not. While there are some factors that add risk, there are many women that have none of these risk factors and still go into preterm labour. The actual cause of preterm labour is still largely unknown.

Around 25-40 percent of preterm births are what we call ‘elective.’ This means they are induced, or delivered by caesarean section early due to an illness in the mother, baby or both. Some common reasons for elective preterm birth are: severe high blood pressure in the mother, poor growth of the baby, problems with the placenta, a baby that is not formed normally or a severe illness in the mother. In these cases an obstetrician will discuss with the parents the benefits of continuing the pregnancy with the risks of ending the pregnancy early. In another 12-15 percent of preterm births the baby has already died or is so abnormal it won’t survive after birth and the labour is often induced.

Around half of all preterm births occur because labour starts ‘spontaneously’. This may begin with contractions or with the ‘waters breaking’ (premature rupture of the membranes). There are several factors associated with spontaneous preterm birth but it can also occur when none of these factors exist:

Infection can cause labour to start or the waters to break.

A weakness in the cervix can lead to premature labour due to the increasing pressure of the growing baby.

Women who are carrying twins triplets or more (multiple pregnancies) are more prone to premature labour. Between 40 and 65 percent of twins and 80 and 95 precent of triplet pregnancies end in preterm birth.

Women who have conceived with assisted conception such as IVF/GIFT are also more likely to experience preterm labour. This is also to do with the fact that these women are more likely to have multiple pregnancies. The National Health and Medical Research Council of Australia recommends that no more than two embryos be put back per cycle because of the increased risk with multiple pregnancies. Increasingly now doctors will encourage women and their partners to consider only putting one embryo back when undertaking IVF because of the complications associated with multiple pregnancies.

Women who have had a previous preterm birth are at increased risk of a preterm birth in a future pregnancy. This is especially the case if the baby was very preterm (under 32 weeks). One preterm birth gives you around a 15 percent chance of having another preterm baby and two preterm births gives you around a 30 percent chance.

Many women who are ‘at risk’ of preterm birth do, however, experience straightforward pregnancies and births. Being at risk does not mean it will happen to you.

Certain social factors such as: very vigorous exercise; excessive use of alcohol, smoking and certain drugs; domestic violence; poor social support; poor access to antenatal care and working very hard may also increase the risk of having a preterm birth.

What can you do?

The National Health and Medical Research Council say there are several things you can do to help prevent a preterm birth, or help improve the outcomes for you and your baby if preterm birth is inevitable.

Seek antenatal care early in pregnancy, especially if you think you are at high risk.

If you are on the IVF/ GIFT program don’t have more than two embryos put back per cycle but one is better.

Get help to quit or cut back smoking.

Avoid exhausting work or very strenuous exercise.

Seek advice if you think you have broken your waters early or are in premature labour and get antibiotic treatment if your waters break preterm.

Plan to give birth in a hospital with a neonatal intensive care unit if you are at very high risk or transfer to one if birth before 33 weeks becomes inevitable.

If your baby is going to be born before 34 weeks have corticosteroids to help mature your baby’s lungs and protect their brain from bleeding.

Can you stop preterm labour?

Most women are very good at diagnosing preterm labour themselves. If you suspect this may be happening to you, you are probably right. If you are bleeding, your waters break or you experience regular contractions (these can feel like period cramps or aches) then phone the hospital and get advice. Drugs called tocolytics are often used when the baby is under 34 weeks to help prolong the pregnancy for a few more days. This can also give the baby a better chance of receiving the benefits of the corticosteroid drugs. Most drugs used in managing preterm labour just prolong pregnancy for a few days rather than stop preterm labour.

What are a preterm baby’s chances of survival?

The amount of care a premature baby will need will depend on how early in the pregnancy they are born, how big they were when they were born and if they were ill when they born. Under normal circumstances every extra week the baby spends growing inside the uterus increases its chances of surviving enormously. Before 24 weeks the chance of a baby surviving is extremely small and the long-term complications if they do survive are great. Routine intensive care is not routinely given. By 28 weeks this chance has increased dramatically and more than 80% of babies will survive if born at a hospital with a Neonatal Intensive Care Unit. Long-term disabilities associated with preterm birth are rare over 30 weeks and increasingly common the earlier the baby is born. Approximately one third of babies born at 24 to 25 weeks and one quarter of babies born at 27 weeks will have some form of disability (commonly problems with eyesight, hearing and movement).

In the first few weeks in the neonatal intensive care the main problems that are encountered by very preterm babies are lack of lung maturity that is needed to maintain enough oxygen in the blood stream. Most babies born before 30 weeks need some help with their breathing. Even at 32 weeks four in every ten babies will need help to breathe. Bleeding in the brain is very rare in babies born after 30 weeks but occurs in one in five babies born before his time. Usually the bleed is small and causes no brain damage but in about one in twenty babies the bleed will be serious enough to cause brain damage and/or death. Premature babies are also very vulnerable to infections, as their defence systems are not properly developed. Antibiotics will be used to treat infections but occasionally they will not be adequate to control the infection.

Survival rates

Completed weeks of pregnancy at birth

Babies Surviving at one year of age in NSW 1992-1997

24 weeks

45-50%

25 weeks

44-65%

26 weeks

57-71%

27 weeks

74-87%

28 weeks

greater than 80%

29 weeks

greater than 90%

30 weeks

greater than 90%

31 weeks

greater than 95%

(NSW Pregnancy & Newborn Services Network, 2000)

How long will a preterm baby be in hospital?

Most preterm babies go home around or slightly before the date they were originally due to be born. It is important that your baby is gaining weight and breastfeeding well before they go home. If your baby has been transferred to a Neonatal Intensive Care Unit then it is highly likely they will be transferred back to a hospital near where you live when they don’t need intensive care any longer.

Can you breastfeed a preterm baby?

Very premature babies will be fed through a drip at first. Breast milk is, however, the best food for all babies and you will be encouraged to express your milk after the baby is born. This can be frozen and given to the baby when they can take feeds though a tube into the stomach. The amount of milk your baby is given will increase gradually over a period of weeks depending how preterm they are. Generally babies begin sucking well between 34 and 36 weeks. Most mothers are breastfeeding by the time their baby comes home.

How does a preterm baby develop?

The development of a preterm baby is of great importance to the parents. Most babies born ten or more weeks early will have developmental checkups. These checkups will keep a track of the baby’s eyesight, hearing and movement. Eyesight and hearing problems can range from mild loss of function to total deafness and blindness. Key development areas that will be examined during developmental check-ups are movement, vision, hearing and language, social development and learning. Of the babies that develop a disability, two thirds will have a mildly disability and will still be able to lead independent lives and one third will have a severe disability that will make them very dependant. To give you an idea, around 30 out of every 100 babies born at 24 to 25 weeks and 25 out of every 100 born at 27 weeks, will have one or more of these disabilities.

How does preterm birth affect parents?

Preterm birth has been described as a crisis and parents often go through a wide range of emotions such as fear, shock, hurt, grief, guilt and a sense of lost control. Parents grieve for lost experiences and lost dreams and have to learn to come to terms with the reality they have been dealt. The roller coaster of emotions that result can be exhausting and confusing and whatever the individual experience, parents need a great deal of support and information to help them through this often unexpected event. Doctors, nurses, midwives, social workers, lactation consultants, chaplains and preterm support groups interact with and support parents through this very difficult time.